You can either create a launcher for this in the main menu, or indeed a script. For launcher go to Control Center -> Main Menu, select a category where you want this command, click New Item and set command to your rdesktop line. Also give it a name, and you are done. (You can click the default icon to change it to something else.)

You could also create a small shell script. Create a text file, for example called Connect.sh, and put the following text in it:

Good to hear this worked for you! Lets stick to English here, so others can read and understand solutions and feedback also Perhaps also note down the Dutch Linux Mint forums: http://forum.linuxmint-nl.org/